1. Field of the Invention
The present invention relates to a control apparatus and program for monitoring a communication network. Particularly, it relates to a system for controlling an MPLS (Multi-Protocol Label Switching) network.
2. Description of the Background Art
Nowadays, a transmission network accommodating various client protocols has been required toward transition to a next-generation network which will perform diversified services.
A method called MPLS (Multi-Protocol Label Switching) in which a frame or packet is transferred while an identifier called label is added to the frame or packet has attracted attention as a method for accommodating various client protocols.
In the next-generation network, high transmission quality is required of a communication path. In a network using a packet transfer method, if traffic exceeding the transfer throughput capacity of each node flows in a certain node, packet loss occurs to lower transmission quality. If traffic is concentrated in a certain node, packet loss occurs though the whole network still has a surplus throughput capacity.
Accordingly, if load can be dispersed or balanced by some method, accommodating efficiency in the whole network can be improved. Or the same traffic as that of the whole network can be accommodated in a network composed of nodes lower in throughput capacity.
A method of exchanging measured values of traffic between nodes and controlling a transfer path based on the exchanged measured values in order to disperse transfer load of respective nodes has been disclosed in JP-A-2007-060467.
On the other hand, lowering of quality due to packet loss is also caused by transmission error of link between respective nodes. A method of giving an error correction code intended for a header of each ATM (Asynchronous Transfer Mode) cell to the cell in an ATM network and correcting error based on this code for the purpose of reducing the transmission error rate of data has been disclosed in ITU-T, I.432.1, “B-ISDN user-network interface-Physical layer specification: General characteristics”, 1999.
By dispersing the packet transfer load and reducing transmission error of each link, transmission quality of a communication path can be improved and the traffic can be accommodated in a network composed of nodes lower in throughput capacity.
When the same error correction method as ITU-T,1.432.1, “B-ISDN user-network interface—Physical layer specification: General characteristics”, 1999 is applied to an MPLS network, another process of calculating an error correction code than a process of determining a transfer destination is required as a packet transfer process
The fact that transmission quality of a communication path is lowered in an MPLS method not using an error correction code will be described first.
In the MPLS method in which an error correction code is not given, if there is 1-bit error in a label, correct path selection cannot be made. As a result, a packet is discarded or transferred to a different node. Because 1-bit error causes 1-packet loss, a BER (Bit Error Rate) increases. An example of packet transfer in the case where error occurs in a label will be described with reference to FIGS. 19 and 20. When a packet 200#6 marked with a label “30” is transferred to 200#7 and the value of the label is changed to “31” due to 1-bit error during the transfer, the packet is discarded if there is no setting that a packet having a label value of “31” to a node B is transferred to a node D, or the packet is transferred to a different node if there is a setting that a packet having a label value of “31” to the node B is transferred to the different node. In any case, packet loss occurs.
The fact that the load based on processing of the error correction code depends on the number of packets which perform label swapping (label swapping with changing value of label) will be described next.
FIG. 20 shows an example of a label using an error correction code. A switching portion of each node calculates a 3-byte error correction code 202 intended for error correction of a 12-byte label 201 and provides the error correction code 202 as a header portion to thereby achieve 1-bit error correction of the label.
Because the error correction code 202 is calculated based on the label 201 as described above, the error correction code 202 must be calculated whenever label swapping is performed. Accordingly, in the MPLS network in which an error correction code is introduced, increase of processing load according to each node in connection with label swapping becomes further larger. If the label swap processing load per node is too large, the processing time per packet becomes long. If the throughput capacity of each node is outstepped, packet delay and packet loss are brought.